1. Technical Field
The present invention relates to a particle detector for the direct or indirect detection of beam-carried particles, such as ions, electrons, energetically neutral particles and photons. The detector is of the kind that includes a body that has a beam-incident surface which is able to release secondary electrons in numbers proportional to the number of particles incident on said surface, and a secondary electron multiplier channel whose inlet opening is located adjacent the beam-incident surface and functions to amplify the number of secondary electrons. The invention also relates to a method of detecting charged particles, such as ions and electrons, in a beam that contains charged and charge-free particles.
2. Description of the Related Art
Secondary electron multipliers are well-known detectors to those skilled in the art, and are used, for instance, in the detection of ions and other particles, such as electrons and energetically neutral particles. In one application, in addition to containing sought-after ions, a gas beam also includes neutral, charge-free particles that are able to interfere with the detection of ions. It is therefore desirable that solely ions strike the detector.
One known method involves generating an electromagnetic field that causes the charged ion-particles to deviate in a direction that differs from the direction of the original gas beam, therewith forming a separate ion beam. This ion beam is then caused to impinge on a detector. Although some ion losses occur when breaking-up the gas beam, the accuracy of the detection process is markedly improved in relation to a measuring or analyzing process that is carried out directly on the original gas beam.
Channel-type secondary electron multipliers are commercially available. These multipliers include a typical flared or funnel-like inlet opening which is intended to receive a particle-carrying beam for detection, wherewith the particles carried by the beam release secondary electrons in numbers proportional to the number of particles present. Released secondary electrons are attracted into an electron multiplier channel and there trigger an electron avalanche which falls onto an anode or collector at the end of the channel, in which the electron charge that has been torn down is measured. The principles of this type of detection are well known to the person skilled in this art and will not therefore be described in more detail in this document.
EP 0 401 879 A2 teaches a secondary electron multiplier in the form of a monolithic, ceramic body that includes a funnel shaped entry port to an electron multiplier channel. The body is provided internally with a semiconductive secondary electron emitting layer along the channel walls. The channel preferably extends three-dimensionally in a spiral path through the body and exits contiguous to an anode. This device is intended to be used for measuring or analyzing a purely ion beam that contains no disturbing or interfering particles.
Important criteria that separate different types of detectors are sensitivity, accuracy, efficiency and response time.
The response time, i.e. the time between two measuring processes, is dependent on the time taken to recharge the channel layer with electrons subsequent to triggering an electron avalanche.
Sensitivity and accuracy are contingent on detector temperature and the electrical conductivity of the detector, among other things. It is essential to cool the detector effectively, which also lengthens the useful life span of the detector.
Efficiency relates to the relative proportion of incident particles that are detected. The object of the present invention is to provide a detector and a method that are more efficient than present-day detectors and methods.